The newest generations of power semiconductor integrated circuits, as shown in FIG. 1 view 110, may use copper metallization pads 102 and/or copper interconnects 104 due to the excellent electrical conductivity of copper. Copper contact pads, especially exposed copper contact pads such as copper pad 102 formed on semiconductor chips such as silicon chip 106, may suffer from reliability issues and degradation problems. Up until now, passivation for copper pads, e.g. organic layer depositions, may not be well integrated. While the copper may be protected, significant and complex problems may occur with respect to probing and wire bonding. Typically, protective passivation for copper pads, such as dielectric materials, e.g. dielectric nitrides or dielectric oxides, may be deposited by standard chemical vapor deposition (CVD) processes. These dielectrics may be or must be relatively thick in order to protect the copper pad 102 and even the side walls and the undercut regions.
FIG. 2 shows images of reliability problems relating to copper pads. Copper pads such as bare copper pad 102 in FIG. 1 may suffer from copper oxidation, which may adversely affect a defined copper surface for wire bonding processes. Inset A of FIG. 2 shows an image of an oxidized copper pad 102D which may suffer from discoloration. Copper pads such as copper pad 102 and/or 102D, if opened, may be oxidized during processing, for example on the way from front end processes to back end processes; and furthermore in the back end, e.g. during sawing. This may reduce or affect the bond quality. For example, copper-to-copper bonds and/or aluminum-to-copper bonds on the copper pad may be affected. In extreme cases, the wires (aluminum and/or copper wires) may no longer be able to be bonded to copper pads, which may sometimes be referred to as a non-stick on pad (NSOP) problem.
Copper structures, e.g. copper contact pads, copper lines or copper vias, may further suffer from reliability issues due to dendrite growth. Leakage current between metal lines may occur because of copper electrochemistry e.g. if inter metal isolation dielectric (IMID) or polyimide passivation fails due to delamination, pores, cracks, or contamination, for example on the bottom IMID interfaces. As shown in insets B and C of FIG. 2, growth of copper structures 208, such as growth of copper dendrites 212, may occur from copper pads 102 or other copper lines. Growth of these unwanted copper structures 208, 212 may be caused by exposure to moisture, e.g. moisture leakage through the passivation layer, such as the protective dielectric, and further due to applied electrical voltages to the copper structures for example during electrochemistry, and even during operation of the device. As a result, in operation, neighboring copper pads and/or tracks and/or lines, may connect to each other along weak passivation interfaces. The copper structures may then be affected by short-circuiting due to dendrite growth and/or filament formation.
These issues may affect or hinder the production of a robust and low cost final copper metallization.